It is known in the art that ABS control systems are activated in response to rough road sections or road irregularities that occur during a braking operation (partial braking) without or prior to the proper wheel lock pressure level being reached. First of all, this causes an unwanted braking pressure reduction the wheel concerned, followed by a pulsed or stepwise braking pressure re-increase and, consequently, unnecessary actuation of the brake valves connected to disturbing valve noises and reductions in comfort and, in certain situation, a loss in deceleration of the vehicle or a longer stopping distance. This is because the original braking pressure level is reached only with time delay in the braking pressure increase phase following the braking pressure reduction induced by the road irregularity.
DE 195 36 105 A1 discloses a method of improving the control behavior of an anti-lock system (ABS) due to a single road irregularity, wherein a road irregularity is inferred from the maximum wheel slip that occurs as a result of the road irregularity on the wheel concerned, and from the duration of pressure reduction until the re-acceleration of the wheel. When a single road irregularity is detected, the braking pressure on the wheel suffering from the single irregularity is re-increased until the wheel acceleration falls below a predetermined limit value.
In the event of a major reduction of the wheel contact force due to a bump or a road irregularity having similar effects, when the brake slip exceeds a predetermined limit value and lasts for a minimum period of time, it is further known from DE 195 30 902 A1 to produce the product of the maximum brake slip and the time period from the commencement of instability until the point of wheel reversal, i.e., the re-acceleration, and to raise the braking pressure increase gradient in the subsequent pressure increase phase if the product exceeds a limit value.